The present disclosure relates to medical interventional systems and methods and more particularly, to valve replacement systems and methods. The long-term clinical effect of valve regurgitation is well recognized as a significant contributor to cardiovascular related morbidity and mortality. In particular, there are two basic classifications of mitral regurgitation (“MR”), primary and secondary. Primary MR results when there is either direct tissue pathology of the valve structures or there is structural damage/alteration of one or more valve structures (leaflets, chordae). Secondary MR results from damage to the myocardium and left ventricle resulting in left ventricular dilatation, and secondary alteration of mitral valve geometry and functional loss of valve competence. Whether valvular in origin leading to a ventricular problem or of ventricular/muscle origin leading to the valvular problem, the effect of high levels of MR is significant on cardiopulmonary physiology, resulting in significantly elevated left atrial pressures and pulmonary pressures, pulmonary congestion, and volume and energy overload effects on the myocardium. This physiology creates significant heart failure symptoms of shortness of breath and decreased physical endurance, ultimately leading to death.
The decision to intervene on a regurgitant mitral valve relates to the level of mitral regurgitation, the symptoms of the patient as an indicator of progressive negative physiologic effect, and the functional status of the left ventricle, specifically ejection fraction. The risk of intervention is weighed against the benefit of MR treatment.
The mitral valve is a therapeutic target of intervention/surgery early in the disease process of primary valvular disease because of MR's deleterious effects on heart/ventricular function if left untreated. For patients with moderate-severe or severe levels of MR combined with even a modest decrease in ejection fraction (“EF”), or the development of symptoms, surgical correction is indicated. In this situation, the risk of surgery in what is an otherwise healthy patient is far outweighed by the beneficial effects of eliminating the long-term negative effects of MR.
A more difficult question has been the patient with secondary or functional mitral regurgitation. In this situation, the patient has pre-existing LV dysfunction combined with heart failure symptoms, and a developing/worsening level of MR. The risks of intervention in this scenario are much greater. The net benefit of surgically intervening to eliminate the MR has not been demonstrated. Symptomatic benefit has been seen, but not a net mortality benefit. Therefore, it is usually contemplated or applied concomitantly when a patient is undergoing coronary artery bypass graft CABG revascularization.
The classification of mitral regurgitation as primary or secondary is a useful to differentiate between the underlying disease processes that led to the incompetent valve. These provide a starting point that can direct the type and timing of an intervention. However, classification is not sufficient to fully describe the issues that direct a therapeutic approach. Because the mitral valve is complex structurally, mechanically, and physiologically, a more detailed description and understanding of the abnormalities associated with mitral regurgitation is needed to direct existing therapies, as well as develop new options for therapy.
Pathologic abnormality of the mitral valve tissue is a common cause of primary mitral regurgitation. Typical pathologies that occur include rheumatic, myxomatous, endocarditis, and Marfan's or other collagen based tissue diseases. Calcification and leaflet thickening are also abnormalities associated with direct tissue level changes in the valve. These can be either part of a primary tissue based disease or result from a long-standing insult to the valve, including regurgitant jetting across the leaflets.
Congenital and acquired structural abnormalities like ruptured chordae, leaflet prolapse, fenestrations, and clefts can also be forms of primary valve disease leading to mitral regurgitation.
Functional MR results from myocardial damage leading to ventricular functional loss and geometric changes that impact the valve coaptation through associated annular dilatation and papillary muscle displacement. In pure functional MR, the valve structures are not pathologic nor have structural defects, but the geometric alteration leads to a loss of coaptation of the mitral valve leaflets, often in the central A2/P2 segment of the valve.
As with many multi-factorial clinical problems, one etiologic element (tissue pathology, structural alterations, functional/geometric changes) may lead to others resulting in a “mixed” picture. This is especially true with mitral regurgitation. In the case of primary MR of either tissue or structural origin, volume overload of the LV can create failure and LV dilatation creating a component of functional MR if the valve is left untreated. In the case of long standing functional MR, tissue changes can be seen such as calcification and thickening caused by the regurgitant jet and high leaflet stresses. Muscle/tissue damage to the myocardium in and around the sub-valvular apparatus can create structural alteration such as ruptured papillary muscles/chordae and prolapse. Excessive tenting of the leaflets associated with significant functional MR can also stress the chords causing rupture.
The net result is that MR is a spectrum disorder with many patients having a mixed picture of valve abnormalities. This is an important factor in the decisions surrounding a mitral valve therapeutic approach, specifically repair or replacement.
The primary goal of any therapy of the mitral valve is to significantly reduce or eliminate the regurgitation. By eliminating the regurgitation, the destructive volume overload effects on the left ventricle are attenuated. The volume overload of regurgitation relates to the excessive kinetic energy required during isotonic contraction to generate overall stroke volume in an attempt to maintain forward stroke volume and cardiac output. It also relates to the pressure potential energy dissipation of the leaking valve during the most energy-consuming portion of the cardiac cycle, isovolumic contraction. Additionally, successful MR reduction should have the effect of reducing the elevated pressures in the left atrium and pulmonary vasculature reducing pulmonary edema (congestion) and shortness of breath symptomatology. It also has a positive effect on the filling profile of the left ventricle and the restrictive LV physiology that can result with MR. These pathophysiologic issues indicate the potential benefits of MR therapy, but also indicates the complexity of the system and the need for a therapy to focus beyond the MR level or grade.
It is also desirable to prevent new deleterious physiology or function of the valve. The procedure and system used to fix the mitral valve ideally should avoid worsening other (non-MR) existing pathologic conditions or creating new pathologic conditions as a result of the treatment of the critical factors to be managed is Stenosis/gradient. That is, if a valve system is used that does not allow for sufficient LV inflow without elevated filling pressures, then critical benefits of MR reduction are dissipated or lost. Moreover, atrial fibrillation is to be avoided as it can result if elevated pressures are not relieved by the therapy, or are created by the system (high pressure results in atrial stress leading to dilatation ultimately leading to arrhythmias). Also, if the procedure results in damage to atrial tissue at surgery, it can result in the negative physiologic effect of atrial fibrillation. Further, one should be aware of the possibility of increased LV Wall Stress (LV geometry). Due to the integral relationship of the mitral valve with LV geometry through the papillary and chordal apparatus, LV wall stress levels can be directly affected resulting in alterations of LV filling and contraction mechanics. Accordingly, a system that does not preserve or worsens the geometry of the LV can counter the benefits of MR reduction because of the alteration of contractile physiology.
It has been generally agreed that it is preferable if the valve can be repaired. Repair of valve elements that target the regurgitant jet only allows for minimal alteration to the valve elements/structures that are properly functioning allowing for the least potential for negatively effecting the overall physiology while achieving the primary goal. Native valve preservation can be beneficial because a well repaired valve is considered to have a better chance of having long standing durability versus a replacement with an artificial valve that has durability limits. Also, while current surgical artificial valves attempt chord sparing procedures, the LV geometric relationship may be negatively altered if not performed or performed poorly leading to an increase in LV wall stress due to an increase in LV diameter. Thus, while preferred and possible for technically competent surgeons, the relatively high recurrence rate of MR due to inadequate repair, the invasiveness of the surgery especially in sick or functional MR patients, and the complexities of a repair for many surgeons lead to a high percentage of mitral operations being replacement.
Conventionally, surgical repair or replacement of the mitral valve is performed on cardiopulmonary bypass and is usually performed via an open median sternotomy resulting in one of the most invasive high risk cardiac surgical operations performed, especially in subpopulations such as functional MR. Therefore, a key improvement to mitral valve operations is to significantly lower the risk and invasiveness, specifically utilizing a percutaneous or minimally invasive technique.
While there have been attempts to replicate existing surgical repair via less invasive surgical or percutaneous methods, given the complexity of repairing the valve surgically, the efforts have largely been deemed lacking in achieving adequate efficacy and have not altered the risk benefit ratio sufficiently to warrant ongoing investment, approval, or adoption. In particular, there has been a general technology failure due to the complexity of anatomy to percutaneously manage with an implant or implantable procedure. The broad spectrum of mitral disease directly influences outcomes with a resulting inability to match technology with pathology. There has also been observed inadequate efficacy with poor surgical replication and safety results. It has also been recognized that percutaneous approaches successful to certain valve procedures, such as aortic valve replacement associated with a single pathology and a relatively circular rigid substrate, mitral valves often suffer from multiple pathologies and a flexible or elastic annular with multiple structures.
Accordingly, what is needed is an effective long lasting MR reduction without creating negative physiologic consequences to the cardio-pulmonary system (heart, lungs, peripheral vasculature) including stenosis, LV wall stress and atrial fibrillation. It is also desirable to be able to perform the operation in a reliable, repeatable, and easy to perform procedure and to have a broadly applicable procedure for both patients and physicians, while employing a significantly less invasive method.
The present disclosure addresses these and other needs.